The present disclosure relates to an electric working machine that includes a three-phase brushless motor.
An electric working machine including a three-phase brushless motor as a driving source is configured to reduce or stop rotation of the three-phase brushless motor by using a so-called short-circuit brake. The short-circuit brake is achieved through three terminals of the three-phase brushless motor to be shorted, which generates a braking force on the three-phase brushless motor.
The short-circuit brake in general use is a three-phase short-circuit control, where a brake current flows into all phases of the three-phase brushless motor. Such a three-phase short-circuit control generates an excessive braking force, which results in increase in force that is applied to an electric apparatus due to the braking force and thus a failure may occur in the electric apparatus.
In respective electric working machines disclosed in Japanese Unexamined Patent Application Publication No. 2013-243824 and Japanese Unexamined Patent Application Publication No. 2017-070102, a two-phase short-circuit control is executed to thereby generate a desired braking force. In the two-phase short-circuit control, only two current paths are completed among three current paths between respective three terminals of a three-phase brushless motor and a positive electrode of a direct-current power source. Alternatively, only two current paths are completed among three current paths between the respective three terminals and a negative electrode of the direct-current power source.
In the two-phase short-circuit control, as shown in FIG. 7, for example, three high-side switches are tuned off. The high-side switches are switching elements that are provided on the three current paths between the respective three terminals corresponding to a U-phase, a V-phase, and a W-phase of the three-phase brushless motor and the positive electrode (H-side) of the direct-current power source.
On the other hand, three low-side switches are tuned on and off in accordance with rotation of the three-phase brushless motor. The low-side switches are switching elements that are provided on the three current paths between the respective terminals of the three-phase brushless motor and the negative electrode (L-side) of the direct-current power source.
To execute the two-phase short-circuit control, used is a rotation sensor that provides detection signals (Hall signals shown in FIG. 7) every time the motor rotates by a specific angle (every 60-degree in electrical angle, in FIG. 7).
In the two-phase short-circuit control, a delay time is set in a timer every time the motor rotates by the specific angle (at every time periods indicated by arrows in FIG. 7) that corresponds to the detection signals from the rotation sensor, and then measurement by the timer is started (a time point t1). The delay time corresponds to a time (a time corresponding to 30 degrees in electrical angle, in FIG. 7) until any of the low-side switches is next switched to an ON-state or an OFF-state.
In response to elapse of the delay time and an end of the measurement by the timer (a time point t2), any of the low-side switches is switched to the ON-state or the OFF-state in accordance with a specific switching pattern.